Agricultural combines are typically equipped with a harvesting head that is disposed at the front of the vehicle to engage crop as the vehicle travels through the field, separate from the ground, and convey it to the threshing, separating, and cleaning systems within the combine vehicle itself.
One of the problems faced by agricultural combines is the necessity of keeping the harvesting head as close as possible to the ground in order to harvest as much of the crop as possible. At the same time, the harvesting head (if it is a corn head) should not be permitted to dig into the ground, or significant damage may result.
The solution to this problem has been the provision of a header height control system to sense the height of the header above the ground and to maintain the header at a constant height. This is done automatically as the vehicle travels through the field with the ground rising and falling underneath the header and the combine.
These systems were originally mechanical, and later mechanical-hydraulic. More recently, these systems have used electrical header height sensors that are connected to digital microprocessors. The digital microprocessors are programmed to receive height signals from the sensors and to control electrohydraulic valves that responsively raise and lower the harvesting head as appropriate.
One problem with these sensors is their ability to handle the rough treatment they receive. The sensors are typically contact sensors with one end attached to the header and the other end dragging over the ground. The combine and header often change direction, from forward to reverse to steering side-to-side. Furthermore, the header can be dropped flat against the ground, smashing the sensor between the header and the ground if no space is provided. All of this can cause severe damage unless the sensor is made large and strong enough (or small and flexible enough) to avoid injury.
U.S. Pat. No. 6,202,395 discloses a header height sensor that is mounted near the forward end of a row crop header point. “Points” are crop row separators designed to travel almost on the ground and to separate two adjacent rows of crop. The point separates the rows of crop the way the tine of a comb separates hair. The sensor is fixed to the underside of a point and includes a flexible sensor arm (40) that is attached to a rotation sensor (48) and has a ball (46) that engages the ground. The sensor arm is made flexible by providing a coil spring (42) as part of its length. In an alternative embodiment, the same flexible sensor arm is attached to a bracket (62) that is disposed between the flexible sensor arm (96) with coiled spring (98). It also has a ball (102) that engages the ground.
This arrangement suffers from several problems. The coil spring (42, 98) that makes the sensor arm (40, 96) flexible is prone to collect plant matter in its coils when it is flexed in a field. As a result it never returns to its original shape and no longer indicates the proper height above ground. Furthermore, the ball (46, 102) tends to gather dirt and plant matter due to its spherical shape. Even further, the ball, being symmetric, has no steering function and lets the lower portion of the arm be deflected left and right over the ground. This lateral deflection poses a particular problem since the shaft of the arm is flexible, and therefore can be bent easily when the ball at the end of the arm is deflected left and right by the soil. This leads to erroneous readings.
U.S. Pat. Nos. 6,883,299 and 7,310,931 are directed to a header height sensor that solves three identified problems. First, some headers do not have recesses for receiving sensors when the harvesting head is lowered to the ground. Second harvesting heads are operated closer to the ground than they were before and therefore provide little space between the bottom of the harvesting head and the ground in which the sensor can operate. Third, as the header gets closer to the ground it is beneficial to sense the height of the harvesting head farther forward, i.e. closer to the front of the harvesting head, thereby permitting the height controller to sense the height and correct the height sooner. To solve these problems, the device has a sensor arm with a special curvature that causes the ground contact point of the arm to move forward toward the front of the harvesting head as the harvesting head gets closer to the ground. The arm is thin and flexible with a tapered cross section so that it can be flattened between the flat ground and the flat bottom of the harvesting head. The arm is made of polyurethane to permit it to be severely bent without being damaged and to return to its original shape. The arm is so light that it requires a supplemental spring to hold the arm down against the ground.
The sensor arrangement of the '299 and '931 patents is suited to platform harvesting heads with flat bottoms that drag along the ground. The sensor arm of these patents avoids using the coil spring of the '395 patent for flexibility, but the resulting curved and flexible arm of the '299 patent is thin and easily damaged.